The present invention relates a package incorporating a pressure venting and related methods of manufacture. In particular although not solely the invention related to packages suitable for applications in microwave cooking.
Packages suitable for applications in cooking are known. Such include packages which are, adapted to allow the cooking of foods contained therein, in a microwave oven.
During the cooking of certain foods in such packages, it is desirable to maintain a level of moisture in order to prevent the foods from cooking dry. The presence of moisture within a package during the cooking of the foods will keep the food moist and more pleasant to the taste.
The common form of microwave package are made of plastic film material and can receive food through a mouth region. Water or other liquid may also be added to the contents whereafter the package is normally sealed to contain its contents and placed in the microwave. Upon the heating it will be appreciated that as a result of heating, the pressure inside of the package will increase. The increase in pressure may be such that the package may rupture and result in the spilling of the contents. Continued cooking after the rupturing may result in the food from cooking dry.
Bags with vent holes to deal with an over pressure whilst still allowing good containment of food also exist. As for example illustrated in U.S. Pat. No. 4,874,620, there is provided a package which allows for fluid to escape from the containment region during microwave cooking.
It is an object of the present invention to provide a package incorporating a pressure venting or to provide method of its manufacture to overcome the abovementioned disadvantages or to at least provide the public with a useful choice.
Accordingly in a first aspect the present invention consists in a bag to define a containment region for heating food contents said bag formed of a multiply plastics film to define a front panel and back panel each having side edges, a mouth edge and a bottom edge wherein said side edges of each panel are sealed and wherein the said bottom edges of each panel are substantially sealed to each other to define a sealed bottom of said bag substantially laterally to the longitudinal mouth to bottom edge direction said bag further comprising
at said sealed bottom, a vent passage to allow the escape of fluid from the containment region of said bag during heating of its food contents, provided between said front or back panels where a region of the internal most ply of said multiply plastic film of at least one of said front or back panels is of a less or non-heat sealable nature to the remainder of the material of the internal most ply at the said scaled bottom.
Preferably said region of the internal most ply is of a different material to the remainder of said internal most ply.
Preferably said different material of said region extends from mouth to bottom edge of one of said front or back panels.
Preferably said inner most ply of one of said front of back panels comprises 3 longitudinally extending (mouth to bottom) strips wherein the intermediate of said 3 strips is of said different material.
Preferably said strips are in immediate juxtaposition one to the next.
Preferably, said intermediate strip is of smaller width (lateral to the longitudinal direction) than either of the other of said 3 strips.
Preferably said intermediate strip is of an oriented polypropylene.
Preferably said others of said 3 strips is of a cast polypropylene.
Preferably said bottom seal is generated by a heat sealing step to seal the front and back panels at said bottom together save for at said region defining the venting passage. Preferably said heat sealing is applied across the entire width of said bag at said bottom, and is at a temperature and/or dwell time sufficient to seal the overlapping layers of the inner most plies of the front and back panels together, save for where the region is defined by said oriented polypropylene.
Preferably said sealing temperature of said bottom is substantially 130 degrees Celsius.
Preferably said front and back panels are provided by a rectangular shaped sheet of said multiply film, folded longitudinally to define the said sides of said bag and wherein two opposite edges of said rectangular sheet have been heat scaled together.
Preferably at least one other ply of film material is provided external of said internal most ply.
Preferably at least one other ply is sealed to said internal most ply.
Preferably said at least one other ply laminated to said internal most ply.
Preferably said at least one other ply is co-extruded with said internal most ply.
Preferably said at least one other ply is of one rectangular shaped film.
Preferably said at least one other ply is of an oriented polypropylene.
Preferably said sealing temperature at which said bottom seal is generated is less than 180 degrees Celsius.
Preferably said bottom or mouth edge at one of the junctions of said intermediate strip with an other of said strips is provided with a notch.
Preferably said notch is of sufficient size to allow the initiation of a tearing of both panels substantially along the said junction.
Preferably said bag is provided with an unsealed mouth region.
Preferably said bag is provided with a sealable mouth region.
Preferably said sealable mouth region is provided by a reclosable profile strip.
Alternatively said bag is provided with a sealed mouth and food contents provided within the containment region thereof.
In a second aspect the present invention consists in a method of providing a vent passage through an edge seal of a bag defined by overlapping front and rear panels of a multiply film material, said method comprising:
heat sealing the entire of at least one overlapping edge of said front and rear panels where said edge seal is to be provided, at a temperature and dwell time which seals said front and back panels together save for a region to define said venting passage where one or both of the overlapping, surfaces of said front and back panel is provided with a material of a non or less heat sealable nature than the remainder of material of said overlapping surfaces.
Preferably said heat sealing of said at least one edge is achieved between heat sealing jaws of a bag forming apparatus, at a temperature of less than the heat sealing temperature of the said region.
Preferably said material of said region is an oriented polypropylene and the remainder of the material is of a cast polypropylene, and the heat sealing temperature is substantially 120 degrees Celsius.
In a further aspect the present invention consist is a sheet of film material for forming a front and back panel to define a bag having a sealed bottom, mouth and side edges, said film material being an assembly of at least two overlapping and integrally bonded plies of plastic wherein one of the outermost of said plies, to be at the inwardly facing surface of said front or back panels incorporates at least one panel of a dissimilar material to the remainder of said outermost ply, said dissimilar material being of a non or less heat sealable nature and positioned to be located at the bottom seal of the bag to be formed from the said sheet.
Preferably said sheet is a rectangular sheet of material.
Preferably said panel of dissimilar material is in juxtaposition with remainder of said outermost ply, and extends from one edge of said sheet to an opposite edge.
Preferably there is one of said panels of dissimilar material.
Preferably said dissimilar material is oriented polypropylene and the material of the remainder of said outermost ply is cast polypropylene.
Preferably there is one other ply to define said assembly, of the same size as the first mentioned said outermost ply.
Preferably said at least one panel is a longitudinal strip oriented in a direction of said panel parallel to the machine direction to be employed for the forming of said bags from said sheet of material.
In a further aspect the present invention consists in a method of producing a bag provided with a venting passage, said method comprising
advancing in a longitudinal direction, a rectangular sheet of a multiply assembly, said assembly being of at least two overlapping plies wherein one ply is of at least 3 panels wherein said panels are in a side by side longitudinally extending relationship, at least one of the intermediate of said at least 3 panels being of a material of a less or non-heat sealable nature to the other of said at least 3 panels,
forming said rectangular sheet into a tube by bringing together the longitudinal edges of said rectangular sheet such that said at least 3 panel side is internal
sealing said longitudinal edges together,
folding said tube into a lay-flat condition such as to proved a front and back panel
heat sealing at a predetermined temperature and dwell time, the leading (substantially transverse to the longitudinal direction) edge of said tube said temperature and dwell time being such as to define, a bottom sealed substantially entirely across the lateral width of said tube at the leading edge save for at least one region to provide a venting passage for said bag defined between said two panels at the at least one intermediate ply
separating a discrete bag from the tube, a bag length from said bottom seal.
Preferably said at least one intermediate panel is an oriented polypropylene and said other of said at least three panels are a cast poly propylene, wherein said heat sealing temperature is in the range of 130 to 180 degrees Celsius.
Preferably said heat sealing temperature is substantially at 130 degrees Celsius.
Preferably said separating of said discrete bag, simultaneously heat seals the leading edge of the tube.
Preferably prior to said separating of said discrete bag, said bag is filed with food contents, wherein the subsequent separating includes a heat sealing separation of the bag.
In a further aspect the present invention consists in a multiply sheet of plastic film material for the purposes of producing a bag according to the methods as hereinbefore described, or of a configuration of a bag as hereinbefore described.
This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
The invention consists in the foregoing and also envisages constructions of which the following gives examples.